(1) Field of the Invention
The present invention relates to a multiplexer for connecting a multi-row ultrasound transducer array to a beamformer. More specifically, this invention relates to an ultrasound imaging system which employs a multi-row transducer array with more elements than the number of channels of the system""s beamformer.
(2) Description of Related Art
In ultrasound imaging, a transducer is used first to transmit ultrasound waves into the medium to be examined, for example a region of the human body, and then to receive the ultrasound echoes from various discontinuities in the medium and to transform them into electrical signals. The electrical signals then undergo a number of processing steps and are eventually transformed into an image which can be displayed on a device such as a cathode ray tube or can be printed in order to be examined by a physician.
Many ultrasound transducers consist of arrays of small piezoelectric elements. In these cases, the transmit operation is controlled by a multi-channel transmit beamformer, which activates with each channel one or a small group of elements applying various delays, amplitudes and wave shapes in order to produce ultrasound beams propagating in the desired direction and focused at a certain depth along that direction.
Subsequently a multi-channel receive beamformer receives on each channel the signal from one or a small number of elements, delays and amplifies the channel signals and sums them to obtain the focused beam from points along the desired direction. In many cases the number of elements of the array is larger than the number of beamformer channels which can be economically provided. A multiplexer is then used to connect subsets of elements to the beamformer channels.
A large class of transducer arrays, known as 1D (one-dimensional) linear or convex arrays, consists of rectangular elements placed next to each other in the azimuthal direction or along a straight or curved line in the image plane. For these arrays the multiplexers are usually designed to select for each beam a group of elements equal to the number of beamformer channels in the system, currently on the order of 32 channels for a low cost system up to 256 channels for a high-end system. More recently multi-row arrays have come into use. Multi-row arrays have at each azimuthal position several elements (one in each row) arranged in the elevation direction, or perpendicular to the image plane. The multi-row arrays allow changing the depth of focus both in the azimuthal and elevational directions, while the 1D arrays have fixed focus in the elevational direction. In addition, the multi-row arrays are advantageous when aberration correction is employed. Multi-row arrays may be used as 1.25D (groups of elements at the same azimuthal position connected together to the same beamformer channels to control the effective element height), 1.5D (elevationally symmetric pairs of elements connected to the same channels to provide true elevational focusing) or 1.75D (each element connected to a different channel, as needed when aberration correction is used). In the 1.5D and 1.75D cases the number of beamformer channels needed in order to maintain the same azimuthal aperture as in the 1D case increases in proportion to the number of row pairs or rows respectively. In order to operate these multi-row arrays without increasing the number of beamformer channels beyond economically acceptable numbers, synthetic aperture techniques are used, where the beam is transmitted multiple times and each time the multiplexer selects a different subaperture for receive, and the beam is synthesized from multiple receive subapertures.
Existing multi-row arrays often implement mutliplexers which do not allow for an optimal selection of advantageous subaperature. In addition, the number of switches in such multi-row arrays is larger that the minimum necessary to implement the necessary multiplexing requirements. There is therefore needed a multiplexer design which allows for the selection of subapertures for a synthetic aperture technique using relatively few switches.
Accordingly, it is an object of the present invention to provide an ultrasound imaging system, and method for using same, which employs a multi-row transducer array with more elements than the number of channels of the system""s beamformer.
In accordance with the present invention, a system for connecting a transducer array to a beamformer via a multiplexer comprises a multiplexer comprising a plurality of numbered switches a transducer array comprising a plurality of elements arranged in a matrix each element associated with at least one of the numbered switches the matrix comprising a plurality of rows and columns the plurality of rows comprising, a plurality of center rows the elements comprising each of the plurality of center rows associated with a unique portion of the numbered switches wherein each of the center row elements is associated with one of the unique portion the numbered switches, a top row the elements comprising the top row associated with a first and second numbered switch the first numbered switch equal to the numbered switch associated with one of the plurality of center rows elements offset in a first direction in relation to the top row element by an offset of L and the second numbered switch equal to the numbered switch associated with one of the plurality of center rows elements offset in a second direction in relation to the top row element by an offset of L, and a bottom row the elements comprising the bottom row associated with a third and forth numbered switch the third numbered switch equal to the numbered switch associated with one of the plurality of center rows elements offset in a first direction in relation to the bottom row element by an offset of L and the fourth numbered switch equal to the numbered switch associated with one of the plurality of center rows elements offset in a second direction in relation to the bottom row element by an offset of L.